Comment 6 for bug 452151

Same behavior for me on 9.10 with same output:

(Do:3374): Wnck-CRITICAL **: wnck_set_client_type got called multiple times.

Could not locate Tomboy on D-Bus. Perhaps it's not running?
Exception in Gtk# callback delegate
  Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception.
System.ArgumentNullException: Argument cannot be null.
Parameter name: element
  at Do.Core.HistogramRelevanceProvider.IncreaseRelevance (Do.Universe.Item element, System.String match, Do.Universe.Item other) [0x00000]
  at Do.Core.ItemExtensions.IncreaseRelevance (Do.Universe.Item self, System.String match, Do.Universe.Item other) [0x00000]
  at Do.Core.Controller.PerformAction (Boolean vanish) [0x00000]
  at Do.Core.Controller.OnActivateKeyPressEvent (Gdk.EventKey evnt) [0x00000]
  at Do.Core.Controller.KeyPressWrap (Gdk.EventKey evnt) [0x00000]
  at Docky.Interface.DockWindow.OnKeyPressEvent (Gdk.EventKey evnt) [0x00000]
  at Gtk.Widget.keypressevent_cb (IntPtr widget, IntPtr evnt) [0x00000]
   at GLib.ExceptionManager.RaiseUnhandledException(System.Exception e, Boolean is_terminal)
   at Gtk.Widget.keypressevent_cb(IntPtr widget, IntPtr evnt)
   at Gtk.Application.gtk_main()
   at Gtk.Application.Run()
   at Do.Do.Main(System.String[] args)